We are requesting support for a Gordon Conference on Extrachromosomal Elements, to be held at Plymouth School July 1 - 5, 1991. The Extrachromosomal Elements Gordon Conference will provide a unique forum for the interchange of ideas among several groups working on parallel problems in biology but who have few occasions for overlap. These groups include those working on prokaryotic plasmid replication and partitioning, on various aspects of viral replication and proliferation, on DNA transposition, and on various steps in the eukaryotic cell cycle, including DNA replication, nuclear biogenesis, and chromosome segregation. While each of these groups is served by a number of specialized meetings during the year, no single meeting brings all of these topics together. This potential for novel and productive interchanges seems to us to be one of the most valuable benefits of a scientific meeting.